Environmental factors including diet and nutrition have been implicated to play a significant role in cancer have been shown to correlate strongly with high per capita intake of fat. Epidemiological studies indicate that Eskimos have a very low rate of death from breast cancer and yet their diet is very high in fat content. One unique feature of the diet of the Eskimos have a very low rate of death from breast cancer and yet their diet is very high in fat content. one unique feature of the diet of the Eskimos is that their diets are high in marine lipids (n-3 fatty acids) and very low in n-6 fatty acids. Recently, three reports indicated high menhaden oil (high in n-3 fatty acids) consumption of rats to be inhibitory on the promotion stage of chemical carcinogenesis. On the other hand, in vitro enhancement of the binding of benz(a)pyrene to hepatic DNA rats fed high menhaden oil diet was reported in one paper. It is therefore possible that high intake of menhaden oil may have different effect on the two stages of carcinogenesis. This proposed study is aimed to differentiate the effect of high intake of menhaden oil on the two stages of carcinogenesis. One hundred and twenty female 4- week old rats will be randomly assigned to 4 diets (5% corn oil-LCO, 5% menhaden oil-LMO. 20% corn oil-HCO, and 20% menhaden oil-HMO) for 4 weeks to determine the effect of high menhaden oil consumption on the initiation stage of carcinogenesis. At the end of the 4- week feeding period, 7,12-dimethylbenz(a)anthracene (DMBA) will be given to each rat (5mg/100 g.b.wt.). Thereafter, all rats regardless of their previous diet will be fed the LCO diet until necropsy, 20 weeks later. To determine the effect of high menhaden oil consumption on the promotion stage of carcinogenesis, 120 female 4-wk old rats will be fed the LCO diet for 4 weeks. Thereupon, DMBA will be administered to each rat as described above. Thirty rats will then be fed each of the same 4 diets for 20 weeks until necropsy. In both studies, 6 weeks after DMBA administration, each rat will be palpated weekly to monitor tumor development. Body weight and feed intake will be measured during the entire study period. Tumor incidence, latency period, tumor yield (# of tumors), and tumor burden (tumor weight) will be measured, calculated, and compared statistically among the 4 groups of rats. This proposed study will indirectly serve an important purposes to the health of general population. One cannot neglect the negative effect of high consumption of n-3 fatty acids if it is present. It is, therefore, important to pursue the proposed study and gain more knowledge on high intake on n-3 fatty acids in relation to cancer development.